Broad Tunability in mechanical properties of closed cellular foams using micro-bubble assembly of Graphene/silica Nanocomposites

Cellular structures are central to the design of lightweight yet strong materials for engineering development. However, the material properties of cellular foams made of specific elements are placed in a narrow range in their density and corresponding mechanical properties. Here, this study presents an innovative design of creating closed-cellular structured (CCS) foams with a wide range of physical controllability. The CCS foams are prepared by assembly of solid bubbles consisting of reduced graphene oxide (rGO) and silica nanoparticles. By varying their compositional ratio, the resulting CCS foams exhibit completely discerned structural morphologies: Rhombic dodecahedral (RDH) internal cells for higher rGO content, whereas a fused face centered cubic (FCC)-like internal cells for a higher content of silica. As such, these tunable CCS foams manifest an extended relationship in density and resulting mechanical properties, spanning from a density of 2.3 mg/cm³ and corresponding Young's modulus of 0.102 MPa (for RDH) to 444.27 mg/cm³ and 180.3 MPa (for fused-FCC). Moreover, silica-containing CCS can exhibit a thermal insulation property with a greatly reduced thermal conductivity (κ) of 48 mW/m·K.